Pigs are moved through a pipeline either by fluid flowing within the pipeline or by a driving unit called a "crawler". The pigs are used as inspection or cleaning devices and are close-fitting within the pipeline.
Generally the pigs are launched at a launch station and after traversing a section of, say, 20 miles of the length of the pipeline, are recovered at a recovery station. Conventionally these stations have entry and exit gates by which they can be connected to and isolated from a pipeline during launch and recovery. Typically a launch is achieved by introducing the pig into a launch pipe section through the entry gate while the exit gate is closed. Thereafter the entry gate is closed, the exit gate is opened and the pig moved from the launch section into the pipeline either by fluid being introduced between it and the closed entry gate or under the power of the crawler. Thereafter the exit gate is closed.
To be assured that the launch has been achieved it is conventional to have a sharp-eared operative listen for the passage of the pig at some location downstream of the exit gate and to signal to a gate operator that the pig is launched. The present invention relates to a device useful in the operation of launching a pig and to a method of launching a pig.
The rate of progression of the pig through the pipeline is optimized by selecting, on a largely empirical basis, the setting of the crawler carrying the pig or, where the pig is moved by fluid flow, by adjusting the pressure of fluid flowing in the line. The device of the present invention is useful in measuring the rate of progression and contemplates a novel method of doing so.
A typical rate of progression of a pig through the pipeline may be about five miles per hour and so a pig can be expected to complete a twenty mile course in about four hours but there is a wide margin of error in this timing for firstly the rate cannot be set with any degree of accuracy and it is not constant throughout the course. To avoid damage to the gates of the recovery station it is necessary to slow the pig down and this is achieved by stationing a sharp-eared individual at a distance upstream of the recovery station to observe the passage of the pig and to have him signal to an operator controlling the rate of progression of the pig that it should be slowed. Thereafter the entry gate to the recovery station is opened while the exit gate is maintained closed and the pig passes into a recovery section of the pipeline. The entry gate is then closed and the pig thereafter removed from the station through the exit gate. The present invention relates to a device useful in the recovery of a pig from a pipeline and to a method of recovering a pig.
Occasionally a pig will become jammed in the pipeline and it then becomes necessary to locate the pig, plug the line upstream and downstream of the pig and cut the section of the pipeline within which the pig is jammed and remove it. This is a particularly time consuming and potentially dangerous operation when the pipeline is buried. To locate the pig, it is conventional to have an operative follow the course of the pig through the pipeline between the launch and recovery stations with a detector.
The present invention seeks to provide a device and a method of using the device which will facilitate the location of a jammed pig within a pipeline.
An inspection pig is one which has sensor means responsive to pipeline characteristics to produce signals which are recorded for later analysis. The pig conventionally has an odometer and a record of the distance travelled by the pig is made alongside the record of the sensor signals so that when analysis of the record of the sensor signals indicates a region of the pipeline with a potentially dangerous flaw, one can, by referring to the record of the odometer, discover that the flaw is a particular distance from the launch point. The problem with this is that the odometer is not accurate and also that it often occurs that there is no accurate map of the path of the pipeline so that to locate the potential flaw becomes difficult.
In U.S. Pat. No. 3,878,453 (Topping) there is shown a device for disposition in a specific geographical location adjacent a pipeline which generates a signal which is received by a pick-up coil carried by the pig which coil is effective to insert into the record made by the pig a characteristic signature which is used to particularly relate the location of the signature on the record to a specific geographical location along the course of the pipeline. This very substantially assists in the locating of flaws on the record since one is able to use the odometer output to measure a distance from reasonably closely spaced such devices. In this way the absolute error produced by the odometer is substantially reduced.
A problem which has arisen with these devices is that the power requirements are quite substantial particularly where it is necessary to put a signal through the pipeline overlay and through the pipeline into a pig. One technique has been to use a motor/generator set but this requires an operator and must be started up at an estimated time of arrival of the pig at the location and shut down after it has passed. Alternatively, batteries have been used but these are not long lasting.
The present invention seeks to provide a device and a method of using that device which are useful in facilitating operation of a device such as that described in the Topping U.S. patent.
According to one aspect of the present invention there is provided apparatus for observing the passage of a pig in a pipeline which comprises sensor means responsive to a change in ambient magnetic field resulting from the passage of a pig, control means operable by said sensor means and a visual signal means, said control means being effective to cause said signal means to become operative as the sensor means responds to the passage of a pig.
It has been found, surprisingly, that a simple dip needle can effectively sense the passage of a pig even in an underground pipeline and the use of such a device as the sensor means is highly desirable because it is rugged and very inexpensive relative to other devices which might be used.
Desirably the control means may be a light sensitive device responsive to changes caused by movement of the dip needle as a pig passes the apparatus, and producing a signal which can be used to control the visual signal means.
The visual signal means is conveniently a spring loaded flag held in a non-signalling position by a triggering device and in such an arrangement the control means may include a light sensitive device producing a signal which can be used to control a solenoid operating the triggering means to permit the flag to move to a signalling position.
According to another aspect of the present invention there is provided apparatus for indicating a change in a magnetic field comprising:
magnetic field sensing means responsive to a change in a magnetic field, the magnetic field sensing means being physically displaced in response to a change in the ambient magnetic field;
means for monitoring the physical displacement of the sensing means, said monitoring means providing a control signal when the sensing means moves a predetermined amount;
indicating means responsive to the control signal for providing a visible indication of the change in the ambient field, said indicating means being observable from a remote location.
According to yet another aspect of the present invention there is provided an indicating device for use with a sensor, said device comprising: a flag;
latch means for retaining the flag in a non-indicating position;
spring loading means coupled to the flag for urging the flag against the latch means;
said latch means being responsive to control signal from the sensor for release said latch means whereby said spring loading means urges the flag to a visible indicating condition.
According to yet a further aspect of the present invention there is provided a transducer for detecting changes in a magnetic field comprising:
a dip needle mounted for rotation in response to a change in magnetic field about an axis;
rotation indicating means coupled for simultaneous rotation with the dip needle for indicating the amount of rotation of the dip needle;
sensor means for detecting the amount of rotation, indicating means and for providing an output signal in response thereto.
It is to be appreciated that to use the device with a pig which would not normally produce a change in ambient magnetic field or which would produce a change not sufficient to be detected, it is possible to mount a magnet on the pig.
According to still another aspect of the present invention there is provided a method of observing the passage of a pig within a pipeline which comprises taking a device which comprises sensor means, preferably in the form of a dip needle, responsive to changes in ambient magnetic field, control means operable by said sensor means and a visual signal means controlled by said control means, disposing the device close to a pipeline in a position at which the sensor means will respond to changes in ambient magnetic field produced by the passage of a pig in the pipeline and observing the visual signal means.
The method may conveniently be used in launching a pig from a launch station and in such a procedure the device is located a little way downstream of the exit gate of the launch station and when a signal that the pig has passed is given by the device, the exit gate is closed.
There is also provided a method of observing the rate of progression of a pig through a pipeline which comprises disposing two of the devices a known distance apart along the route of the pipeline, recording the elapsed time between when the upstream one of the devices signals the passage of the pig and the downstream one of the devices gives such a signal and calculating the average speed of the pig in covering the known distance.
Additionally there is provided a method of finding a jammed pig which comprises disposing a plurality of the devices along that part of the route of the pipeline over which the pig is intended to travel, finding the most downstream one of the devices which signals that the pig has passed and searching for the pig over that portion of the pipeline between the most downstream one of the devices which signals that the pig has passed and the next downstream one of the devices.
Further according to this invention there is provided a method of inspecting a pipeline for potentially dangerous flaws with a pig which comprises fixing a signal sending device at a known location along a section of the pipeline to be inspected, entering the signal produced by that device on the inspection record produced by the pig, disposing a device for signalling the passage of a pig upstream of the signal sending device and completing a power supply to the signal sending device only when the signal indicating the passage of the pig is given. Preferably the completion of the power supply can be effected automatically in response to a signal generated by the device for signalling the passage of the pig. Preferably a fixed interval timer is associated with this power supply so that it is switched off automatically after the fixed interval.
According to another aspect of this invention there is provided a method of recovering a pig at a recovery station which comprises disposing a device for observing the passage of a pig upstream of the recovery station, reducing the speed of the pig upon the pig passing said device and opening the entry gate of the receiving station.